The present invention relates to a vehicle alternator, and more specifically to a stator structure thereof.
FIG. 9 is a side cross-sectional view of a conventional alternator, and FIG. 10 is a perspective view illustrating a rotor portion thereof.
This alternator comprises a case 33 composed of a front bracket 31 and a rear bracket 32 which are made of aluminum, a shaft 35 provided within a case 33 and having a pulley 34 secured at one end, a rotor 36 of lundell type secured to this shaft 35, fans 37 secured to both side faces of this rotor 36, a stator 38 fixed to an inner wall face within this case 33, a slip ring 39 fixed to the other end portion of the shaft 35 for supplying an electric current to the rotor 36, a pair of brushes 40 for scrubbing this slip ring 39, a brush holder 41 containing these brushes 40, a commutator 60 electrically connected to the stator 38 for rectifying the alternating current produced in the stator 38 to direct current, a heat sink 42 fitted into the brush holder 41, and a regulator 43 attached to this heat sink 42 for regulating the magnitude of alternating voltage produced in the stator 38.
The stator 38 comprises a stator core 44, and a stator coil 45 for generating an alternating current by changes of the magnetic flux from a rotor coil, as described below, along with the rotation of the rotor 36, with a conducting wire wound around this stator core 44.
The rotor 36 comprises a rotor coil 46 for producing the magnetic flux by passing the electric current, and a pole core 47, provided over this rotor coil 46, having the magnetic pole formed by the magnetic flux.
The pole core 47 is composed of a first pole core body 48 and a pole core body 49 which are paired and mated alternately. The first pole core body 48 and the pole core body 49 are constituted integrally of a plurality of claw-like magnetic pole pieces 50, 51 having a pawl shape which are disposed evenly around the peripheral portion thereof and project in one direction, with a thick disk-like bottom portion made of iron as a base. Adjacent claw-like magnetic pole pieces 50, 51 are disposed with a certain magnetic pole spacing H to prevent the magnetic flux from leaking between both pieces.
Since the conventional vehicle alternator is constituted as above, in a claw pole rotor-type alternator, a magnetic flux which passes from the rotor to the stator and is referred to as a leakage flux is routed over the inner peripheral surface of stator iron core along the axial direction into the opposite pole of the rotor. This is caused by virtue of the structure of claw pole, decreasing the magnetic flux that is effective for the generation of power, and lowering the output. Since it produces the pulsation of magnetic flux, it will fluctuate the generated voltage and disorder the output waveform, causing the ripple of generated voltage in the vehicle alternator, and the electromagnetic noise to occur to have a detrimental effect on the external apparatus.
The pulsation of magnetic flux over the inner peripheral surface of stator iron core might increase the fluctuation of magnetic exciting force at an air gap portion, deteriorating the electromagnetic sound which is produced due to resonance of the stator.
It should be noted that in the conventional example for decreasing the leakage flux as above described, there is an art of having two slots for every pole and every phase as disclosed in the Unexamined Japanese Patent Application Publication No. Hei 4-26345 publication, but it was difficult to perform the winding because of the multiple slots.
This invention has been achieved to resolve the above-mentioned problems, and an object of the invention is to provide a vehicle alternator which can provide the greater output, less ripple and less electromagnetic sound by reducing the leakage flux without providing multiple slots.
A vehicle alternator according to aspect 1 of this invention comprises a rotor provided within a case and having claw-like magnetic pole pieces, a stator fixed within the case, and a commutator electrically connected to the stator, wherein the magnetic reluctance of the axial central part of teeth in the stator is increased.
A vehicle alternator according to aspect 2 comprises a rotor provided within a case and having claw-like magnetic pole pieces, a stator fixed within the case, and a commutator electrically connected to the stator, wherein the magnetic flux passing cross section of the axial central part of teeth in the stator is decreased.
A vehicle alternator according to aspect 3 comprises a rotor provided within a case and having claw-like magnetic pole pieces, a stator fixed within the case, and a commutator electrically connected to the stator, wherein a concave portion is provided at the tip of the axial central part of teeth in the stator.
A vehicle alternator according to aspect 4 comprises a rotor provided within a case and having claw-like magnetic pole pieces, a stator fixed within the case, and a commutator electrically connected to the stator, wherein a recess portion is provided in the axial central part of teeth in the stator and on either forward or backward face in the rotational direction of the rotor.
A vehicle alternator according to aspect 5 comprises a rotor provided within a case and having claw-like magnetic pole pieces, a stator fixed within the case, and a commutator electrically connected to the stator, wherein a nonmagnetic material is provided in the axial central part of teeth in the stator.